A lithium ion battery separator and preparation method thereof

Abstract

The present invention discloses a lithium-ion battery separator and a preparation method thereof, belonging to the technical field of lithium-ion battery materials. The lithium-ion battery separator comprises a base film and a functional coating coated on at least one side of the base film; the functional coating comprises nanofibers and inorganic particles; the nanofibers are non-linear structures, the nanofibers of the non-linear structure are interwoven, interlaced and entangled with each other to form a hierarchical porous structure, and the inorganic particles are filled in the hierarchical porous structure. The present invention uses non-linear nanofibers as a skeleton support and fills inorganic particles inside, which not only makes it more difficult for particles to fall off when the separator is mechanically damaged, but also improves the liquid retention of the separator; at the same time, the non-linear fiber structure not only enhances the nanofiber coating ability of the inorganic particles, but also limits the relative movement between the fibers, improves the thermal stability and mechanical properties of the separator, and at the same time can reduce the separator density and improve the battery energy ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and more specifically, to a lithium ion battery separator and a preparation method thereof. Background Art

[0002] The development of lithium-ion batteries is getting faster and faster, and has now expanded from 3C home appliances to large-scale power equipment such as new energy vehicles, energy storage, and large drones. The main components of lithium-ion batteries are positive electrodes, negative electrodes, electrolytes, and diaphragms. The diaphragm is a key component of the battery, responsible for isolating the positive and negative electrodes to avoid short circuits, absorbing and storing electrolytes, and ensuring the permeability of lithium ions. At present, lithium-ion batteries are constantly pursuing large capacity and high specific energy, which puts higher requirements on the physical properties of the diaphragm. Therefore, improving the mechanical properties and thermal stability of the diaphragm is an important research direction.

[0003] Inorganic particles are currently commonly used coating materials and can provide performance support for the base film, but the performance of commonly used diaphragms is unstable at high temperatures and cannot suppress the occurrence of thermal runaway. For example, the functional battery diaphragms invented by Xu Guiying and others, such as the modified composite diaphragms disclosed in the Chinese patent application number 202111572973.9, all have the phenomenon that the fibers cannot fully wrap the inorganic particles. When subjected to external forces, the solid particles are easy to fall off from the fibers inside the coating, and the stability of the coating cannot be guaranteed. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and to provide a lithium-ion battery separator and a preparation method thereof. The functional coating contains non-linear nanofibers as a skeleton support and is filled with inorganic particles. When the coating is subjected to external force, the non-linear nanofibers are stacked on each other to enhance the mechanical properties and thermal stability of the separator. At the same time, the stability of the inorganic particles in the fiber layer can be enhanced, thereby ensuring the high-temperature stability of the separator.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A lithium-ion battery separator, comprising a base film and a functional coating coated on at least one side of the base film; the functional coating comprises nanofibers and inorganic particles; the nanofibers are non-linear structures, the nanofibers of the non-linear structure are interwoven, interlaced and entangled with each other to form a hierarchical porous structure, and the inorganic particles are filled in the hierarchical porous structure; the surface of the nanofibers has a protruding structure; the coverage rate of the protruding structure on the surface of the nanofibers is 8% to 30%; a method for preparing a lithium-ion battery separator, comprising the following steps:

[0007] (1) dissolving the polymer in a solvent to obtain a spinning solution with a concentration of 7% to 12%;

[0008] (2) electrospinning the spinning solution, with a positive electrode voltage of 7KV~28KV, a negative electrode receiving voltage of -1KV~-5KV, a distance between the transmitter and the receiving substrate of 10cm~30cm, a 5ml~20ml syringe, and an infusion speed of 0.005mm / min~0.030mm / min, to obtain nanofibers;

[0009] (3) mixing the nanofibers with water, crushing them at high speed, and then homogenizing them under high pressure to obtain a mixed liquid;

[0010] (4) adding inorganic particles to the mixed solution and dispersing them at high speed to obtain a coating slurry;

[0011] (5) The coating slurry is coated on the surface of the base film, and then baked to obtain the lithium-ion battery separator.

[0012] Optionally, the functional coating also includes a polymer surfactant and an adhesive.

[0013] Optionally, the functional coating includes the following components in percentage by mass: 0.01% to 11.0% of nanofibers, 80% to 99.99% of inorganic particles, 0.01% to 10.0% of high-molecular-weight surfactants, and 1% to 10% of adhesives.

[0014] Optionally, the functional coating includes the following components in percentage by mass: 0.01% to 8.0% of nanofibers, 82% to 99% of inorganic particles, 0.02% to 5.0% of high-molecular-weight surfactants, and 2% to 8% of adhesives.

[0015] Optionally, the non-linear structure of the nanofibers includes bends and / or spirals.

[0016] Optionally, the protrusion structure includes a regular protrusion structure and / or an irregular protrusion structure.

[0017] Optionally, the shape of the protrusion structure includes streamline shape or spindle shape.

[0018] Optionally, the shape of the inorganic particles includes at least one of a sphere, a regular polyhedron and an irregular polyhedron.

[0019] Optionally, the number of layers of the functional coating is 1 to 2 layers.

[0020] Optionally, the base film has a thickness of 1 μm to 40 μm.

[0021] Optionally, the thickness of the functional coating is 0.1 μm to 19 μm.

[0022] Optionally, the nanofiber has a diameter of 10 nm to 1000 nm and a length of 20 μm to 30 μm.

[0023] Optionally, the average diameter D50 of the inorganic particles is 10 nm to 3 um.

[0024] Optionally, the pore sizes of the hierarchical porous structure are micropores and mesopores.

[0025] Optionally, the material of the nanofiber includes one or more of polyimide nanofiber, aramid nanofiber, polyetherimide nanofiber, polyamide-imide, polybenzimidazole nanofiber, polyetheretherketone nanofiber, polyphenylene sulfide nanofiber and polyvinylidene chloride.

[0026] Optionally, the material of the inorganic particles includes one or more of aluminum oxide, boehmite, magnesium hydroxide, silicon dioxide, silicon carbide, zirconium oxide and oxide solid electrolyte.

[0027] Optionally, the polymer surfactant includes one or more of polycarbonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium polyacrylate, polyvinyl alcohol, fluoroalkyl methoxy ether alcohol, fluoroalkyl ethoxy ether alcohol, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, polyoxyethylene alkylamide, fluorine-containing carboxylates, triethyl phosphate, fluorine-containing sulfonates, potassium polyacrylate and polyethylene glycol.

[0028] Optionally, the adhesive includes one or more of styrene-butadiene latex, styrene-acrylic latex, polyvinyl acetate, polyvinyl alcohol, polyethyl acrylate, polybutyl methacrylate, ethylene-vinyl acetate copolymer and polyurethane.

[0029] Optionally, the coating of step (5) includes: flattening the base film on a manual coating machine, pouring the coating slurry on the head side for coating, using a 10μm~500μm wire rod, coating at a speed of 1mm / s~50mm / s, and then baking to obtain the lithium-ion battery separator.

[0030] Optionally, the coating of step (5) includes: coating the coating slurry on both sides of the base film by gravure roller coating, with a coating speed of 5 m / min~140 m / min and an oven temperature of 35°C~120°C.

[0031] Optionally, the step (4) further includes: mixing the inorganic particles and water, and then adding a polymer surfactant to obtain a slurry; mixing the nanofibers with water, and then adding the slurry to perform high-speed dispersion for 5 min to 35 min, and then adding an adhesive to continue dispersing for 15 min to 40 min to obtain a coating slurry.

[0032] Optionally, the rotation speed of the high-speed crushing is 10000rpm~24000rpm, and the time of the high-speed crushing is 10min~40min.

[0033] Optionally, the pressure of the high-pressure homogenization is 500 bar to 1500 bar, and the time of the high-pressure homogenization is 10 min to 30 min.

[0034] Optionally, the baking temperature is 45° C. to 90° C.; and the baking time is 1 min to 20 min.

[0035] Implementing the embodiments of the present invention will have the following beneficial effects:

[0036] The present invention uses non-linear nanofibers as a skeleton support and fills the interior with inorganic particles, which not only makes it more difficult for particles to fall off when the diaphragm is mechanically damaged, but also improves the liquid retention of the diaphragm; at the same time, the non-linear fiber structure not only enhances the nanofiber coating ability of the inorganic particles, but also limits the relative movement between the fibers, thereby improving the thermal stability and mechanical properties of the diaphragm, and at the same time can reduce the diaphragm density and improve the battery energy ratio; and the preparation method of the present invention is green and environmentally friendly, simple in process, safe, low in cost and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a SEM image of the fiber used in the examples of the present invention.

[0038] Figure 2 This is a SEM image of the lithium-ion battery separator of Example 1 of the present invention.

[0039] Figure 3 This is a SEM image of the lithium-ion battery separator of Example 2 of the present invention.

[0040] Figure 4 This is a SEM image of the lithium-ion battery separator of Example 3 of the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0042] Example 1

[0043] The inorganic particles are alumina, purchased from the domestic manufacturer Jiangxi Qihua, model QH-A43, D50 is 0.7um; the PVDF powder is French Arkema PVDF LBG; the adhesive is ABE-5 from Sichuan Yindile Materials Technology Group Co., Ltd.

[0044] The method for preparing the lithium ion battery separator of this embodiment comprises the following steps:

[0045] Take 2g PVDF powder, add 18g DMAc, heat and stir at 5℃ for 4h to prepare a 10% concentration PVDF-DMAc solution. Use a 10ml syringe to absorb a certain amount of PVDF-DMAc solution, place it on the electrospinning machine, set the spinning machine parameters to negative voltage -3.6kv, positive voltage 12kv, ejection speed 0.010mm / min, and the transmitter is 20cm away from the receiver. After the fiber preparation is completed, collect the fibers in a beaker and weigh them. After adding deionized water in proportion, use a high-speed crusher at 14000rpm to crush for 20min. Pour the crushed fiber mixture into a high-pressure homogenizer and crush it at a pressure of 500bar for 15min to obtain the following. Figure 1 The nanofibers shown have a diameter of 10 nm to 1000 nm and a length of 20 μm to 30 μm.

[0046] Weigh 1 g of the mixed solution with a fiber content, add it to the alumina slurry, use a high-speed stirrer to disperse it for 25 minutes, then add 2.7 g of adhesive ABE-5, and continue stirring for 30 minutes.

[0047] Spread the 9um PE base film (air permeability value 168s) flat on the manual coating machine, pour the mixed slurry on the side of the machine head, use a 20μm wire rod, and coat at a speed of 5mm / s. After coating, put it in an 85℃ oven and bake for 1 minute to obtain the following Figure 2 Lithium-ion battery separator shown.

[0048] The lithium-ion battery separator of this embodiment includes a base film and a functional coating coated on at least one side of the base film; the functional coating includes nanofibers and inorganic particulate aluminum oxide; the nanofibers are curved and stacked non-linear structures, and the nanofibers of the non-linear structure are interwoven, intertwined and entangled with each other to form a hierarchical porous structure, the pore size of the hierarchical porous structure is micropores and mesopores, and aluminum oxide is filled in the hierarchical porous structure.

[0049] The surface of the nanofiber has a protrusion structure; the protrusion structure includes a regular protrusion structure and an irregular protrusion structure, and the shape of the protrusion structure includes a streamlined shape or a spindle shape; the coverage rate of the protrusion structure on the surface of the nanofiber is 17%.

[0050] The number of layers of the functional coating is 1, the thickness of the base film is 1 μm to 40 μm, and the thickness of the functional coating is 0.1 μm to 19 μm.

[0051] Example 2

[0052] PI powder was purchased from Evonik, France, model P84 NT2; inorganic particles were selected from alumina, purchased from the domestic manufacturer Jiangxi Qihua, model QH-A43, D50 is 0.7um; CMC: Nippon Paper ML500LC; adhesive, ABE-5 from Sichuan Indile Materials Technology Group Co., Ltd.; high-resolution surfactant: sodium dodecylbenzene sulfonate, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0053] The method for preparing the lithium ion battery separator of this embodiment comprises the following steps:

[0054] Weigh 8g DMAc solution, add 2g PI powder, stir at 60℃ for 4h in a stirring tank to prepare a 20% PI-DMAc solution. Add the solution into a 10ml syringe and put it into the electrospinning equipment. Set the spinning machine parameters as negative electrode receiving voltage -4.2kv, positive electrode voltage 10kv, ejection speed 0.008mm / min, and the transmitter is 23cm away from the receiver.

[0055] After the fiber preparation is completed, the fibers are collected in a beaker and weighed, 10 g of deionized water is added, and the fibers are crushed for 25 min using a high-speed crusher at 14,000 rpm. The crushed fiber mixture is poured into a high-pressure homogenizer and crushed for 10 min at a pressure of 500 bar. The crushed fibers are filtered and the filter cake is dried in an oven at 80°C for 30 min.

[0056] Take 9.6g of deionized water, add 0.4g of CMC powder, stir mechanically at a speed of 1000rpm, stir for 30min and then let stand to degas.

[0057] Weigh 19g of alumina, add 20g of deionized water, use a sand mill at 2000rpm for 15min, then add 10g of 4% CMC solution and stir at 1000rpm for 30min, then add 1g of dried fiber and continue stirring for 30min.

[0058] After stirring, 2.8 g of adhesive ABE-5 and 1 g of 1% sodium polyacrylate solution were added to the alumina solution and stirred at 500 rpm for 30 min.

[0059] The mixed slurry was coated on both sides of a 9um PE base film (air permeability 168s) by gravure roller coating. The single-sided coating thickness of inorganic particles and nanofibers was 3um. The coating speed was 10m / min and the oven temperature was 55°C. Figure 3 Lithium-ion battery separator shown.

[0060] The lithium-ion battery separator of this embodiment includes a base film and a functional coating coated on at least one side of the base film; the functional coating includes nanofibers and inorganic particulate aluminum oxide; the nanofibers are curved and stacked non-linear structures, and the nanofibers of the non-linear structure are interwoven, intertwined and entangled with each other to form a hierarchical porous structure, the pore size of the hierarchical porous structure is micropores and mesopores, and aluminum oxide is filled in the hierarchical porous structure.

[0061] The surface of the nanofiber has a protrusion structure; the protrusion structure includes a regular protrusion structure and an irregular protrusion structure, and the shape of the protrusion structure includes a streamline shape or a spindle shape; the coverage rate of the protrusion structure on the surface of the nanofiber is 22%.

[0062] Example 3

[0063] PMIA powder was purchased from China Taihe New Materials Group Co., Ltd., model number is Taimeida® meta-aramid raw white staple fiber; the inorganic particles are boehmite, purchased from Anhui Yishitong Materials Technology Co., Ltd., model number: BG601, D50 is 0.7um, CMC: Nippon Paper ML500LC; the adhesive is LCH107 from Sichuan Indile Materials Technology Group Co., Ltd., and the high-scoring surfactant: sodium polyacrylate was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0064] The method for preparing the lithium ion battery separator of this embodiment comprises the following steps:

[0065] Weigh 9g DMAc solution, add 1g PI powder to it, stir at 60℃ for 4h in a stirring tank to prepare a 20% concentration PMIA-DMAc solution. Add the solution into a 10ml syringe and put it into the electrospinning equipment. Set the spinning machine parameters as negative electrode voltage -3kv, positive electrode voltage 12kv, ejection speed 0.008mm / min, and the transmitter is 23cm away from the receiver.

[0066] After the fiber preparation is completed, the fibers are collected in a beaker and weighed, 10 g of deionized water is added, and the fibers are crushed for 25 min using a high-speed crusher at 14,000 rpm. The crushed fiber mixture is poured into a high-pressure homogenizer and crushed for 10 min at a pressure of 500 bar. The crushed fibers are filtered and the filter cake is dried in an oven at 80°C for 30 min.

[0067] 3.5 g of boehmite powder was added to 5 g of deionized water, and then 3 g of 1% sodium polyacrylate solution and 1 g of crushed PMIA fiber were added. After being evenly dispersed, 0.5 g of adhesive was added to make a slurry, which was coated on one side of a 12 μm PE base film by gravure roller coating. The mixed coating with a thickness of 3 μm was coated at a coating speed of 5 m / min and an oven temperature of 50 °C to obtain the following Figure 4 Lithium-ion battery separator shown.

[0068] The lithium-ion battery separator of this embodiment includes a base film and a functional coating coated on at least one side of the base film; the functional coating includes nanofibers and inorganic particulate aluminum oxide; the nanofibers are curved and stacked non-linear structures, and the nanofibers of the non-linear structure are interwoven, intertwined and entangled with each other to form a hierarchical porous structure, the pore size of the hierarchical porous structure is micropores and mesopores, and aluminum oxide is filled in the hierarchical porous structure.

[0069] The surface of the nanofiber has a protrusion structure; the protrusion structure includes a regular protrusion structure and an irregular protrusion structure, and the shape of the protrusion structure includes a streamline shape or a spindle shape; the coverage rate of the protrusion structure on the surface of the nanofiber is 8%.

[0070] Example 4

[0071] PI powder, purchased from Evonik Industries AG, Germany, model P84® NT2; inorganic particles selected from boehmite, purchased from Anhui Yishitong Materials Technology Co., Ltd., model: BG601, D50 is 0.7um. CMC: Nippon Paper ML500LC; adhesive, selected from Sichuan Yindile Materials Technology Group Co., Ltd. LCH107, high-scoring surfactant: polyacrylic acid sodium, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0072] The method for preparing the lithium ion battery separator of this embodiment comprises the following steps:

[0073] Weigh 8g DMAc solution, add 2g PI powder, stir at 60℃ for 4h in a stirring tank to prepare a 20% PI-DMAc solution. Add the solution into a 10ml syringe and put it into the electrospinning equipment. Set the spinning machine parameters as negative voltage -3kv, positive voltage 18kv, ejection speed 0.005mm / min, and the transmitter is 23cm away from the receiver.

[0074] After the fiber preparation is completed, the fiber is collected and weighed in a beaker, 20g of deionized water is added, and the fiber is crushed for 25 minutes using a high-speed crusher at 14000rpm. The crushed fiber mixture is poured into a high-pressure homogenizer and crushed for 10 minutes at a pressure of 500bar. The crushed fiber is filtered and the filter cake is dried in an oven at 80℃ for 30 minutes.

[0075] 3.5g of boehmite powder was added to 5g of deionized water, and then 3g of 1% sodium polyacrylate solution and 1.5g of crushed PMIA fiber were added. After uniform dispersion, 0.5g of adhesive was added to make a slurry, which was coated on one side of a 12um PE base film using a gravure roller coating method. A mixed coating with a thickness of 3um was applied. The coating speed was 5m / min and the oven temperature was 50°C.

[0076] The lithium-ion battery separator of this embodiment includes a base film and a functional coating coated on at least one side of the base film; the functional coating includes nanofibers and inorganic particulate aluminum oxide; the nanofibers are curved and stacked non-linear structures, and the nanofibers of the non-linear structure are interwoven, intertwined and entangled with each other to form a hierarchical porous structure, the pore size of the hierarchical porous structure is micropores and mesopores, and aluminum oxide is filled in the hierarchical porous structure.

[0077] The surface of the nanofiber has a protrusion structure; the protrusion structure includes a regular protrusion structure and an irregular protrusion structure, and the shape of the protrusion structure includes a streamline shape or a spindle shape; the coverage rate of the protrusion structure on the surface of the nanofiber is 30%.

[0078] Comparative Example 1

[0079] This comparative example provides a lithium-ion battery separator coated with a traditional ceramic slurry, the separator thickness is 12 μm, wherein the base membrane is a 9 μm PE base membrane (air permeability value 168 s) and a polypropylene base membrane with a porosity of 47%; a traditional ceramic slurry is used to coat one side to form a coating with a thickness of 3 μm.

[0080] Comparative Example 2

[0081] This comparative example provides a lithium-ion battery separator coated with a traditional fiber-ceramic composite slurry, the separator thickness is 12μm, wherein the base membrane is a 9um PE base membrane (air permeability value 168s) with a porosity of 47%; the fiber is a linear polymer fiber with a wire diameter of 100nm-1000nm; and a traditional ceramic slurry is used to coat one side to form a coating with a thickness of 3μm.

[0082] Test Case

[0083] The roller process of the diaphragm in the winding and slitting processes is simulated to test the adhesion of the diaphragm to the negative electrode sheet after hot pressing (2MPa, 90s) before and after slitting, that is, the peel strength; shrinkage rate; diaphragm wettability; tensile strength measurement.

[0084] Test method for adhesion of diaphragm to negative electrode:

[0085] 1) Sample preparation: First, lay a 10cm×15cm separator on a 10cm×14cm negative electrode, and place a flat steel plate under the electrode. Use a flat hot press to press at a pressure of 2MPa for 90s.

[0086] 2) Test: Use a universal tensile machine in 180 degree peel mode to measure the peel strength between the diaphragm and the electrode.

[0087] Shrinkage

[0088] The modified composite membrane was cut into 5cm×5cm diaphragms and placed in an oven at 150℃ and 200℃ for 30min, respectively. The thermal shrinkage test method was based on the standard of GBT36363-2018. The thermal shrinkage of the membrane was measured in the longitudinal direction (MD) and transverse direction (TD), and the higher value of the thermal shrinkage in MD and TD was defined as the thermal shrinkage of the membrane.

[0089] Membrane wettability

[0090] Use a mold to cut the diaphragm into 2cm×10cm strips, hang the strips on a lifting platform, prepare the electrolyte and place it on the table, adjust the height of the strips until the bottom is in contact with the electrolyte, and measure the climbing height of the electrolyte 5min and 10min after contact.

[0091] Measurement of tensile strength

[0092] The method for measuring the tensile strength of the modified composite diaphragm is in accordance with the standard of GBT36363-2018. A type 2 sample with a width of (15±0.1) mm, an initial distance between the clamps of (100±5) mm, a test speed of (250±10) mm / min, and the maximum strength value during the sample stretching process is taken as the tensile strength to record and compare. The tensile strength is measured in the longitudinal direction (MD) and transverse direction (TD) respectively, and then the lower value of the tensile strength in MD and TD is defined as the tensile strength of the modified composite diaphragm.

[0093] Among them, the 200℃ tensile strength refers to the modified composite diaphragm being kept at 200℃ for 30 minutes to test the thermal shrinkage, and then the specimens are cut and the tensile strength is tested according to the above method.

[0094] Diaphragm air permeability test

[0095] The Japanese Industrial Standard is currently used in the diaphragm industry, which is to test the time required for 100mL of air to pass through a 1 square inch diaphragm under a pressure of 1.22kPa. Use a mold to cut the diaphragm into 5cm×5cm samples, and measure the air permeability time on a diaphragm air permeability tester.

[0096] Table 1 Performance comparison of Examples 1-4 and Comparative Examples 1-2

[0097]

[0098] By comparison, the peel strength of Examples 1 to 4 and Comparative Examples 1-2 indicates that the addition of non-linear nanofibers to the coating improves the adhesion between the diaphragm and the coating.

[0099] By comparison, the thermal shrinkage of Examples 1-4 is lower than that of Comparative Examples 1-2, indicating that the introduction of non-linear nanofibers can delay the thermal shrinkage of the diaphragm in a high temperature environment and improve the thermal stability of the battery diaphragm.

[0100] By comparison, the electrolyte climbing heights of Examples 1-4 and Comparative Examples 1-2 indicate that the introduction of non-linear nanofibers can significantly improve the liquid absorption and night retention properties of the diaphragm.

[0101] By comparison, the air permeability time and tensile strength of Examples 1-4 and Comparative Examples 1-2 are compared, which shows that the introduction of non-linear nanofibers in the coating can enhance the mechanical strength of the diaphragm without changing the air permeability of the diaphragm itself, and the air permeability characterizes that the composite diaphragm has a porous structure.

[0102] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A lithium ion battery separator, characterized in that: The lithium-ion battery separator comprises a base film and a functional coating coated on at least one side of the base film; The functional coating comprises nanofibers and inorganic particles; The nanofibers are non-linear structures, the nanofibers in the non-linear structure are interwoven, intertwined and entangled with each other to form a hierarchical porous structure, and the inorganic particles are filled in the hierarchical porous structure; The surface of the nanofiber has a protrusion structure; The coverage rate of the protrusion structure on the surface of the nanofiber is 8% to 30%; The method for preparing the lithium ion battery separator comprises the following steps: (1) dissolving the polymer in a solvent to obtain a spinning solution with a concentration of 7% to 12%; (2) electrospinning the spinning solution, with a positive electrode voltage of 7KV to 28KV, a negative electrode receiving voltage of -1KV to -5KV, a distance between the emitter and the receiving substrate of 10cm to 30cm, a 5ml to 20ml syringe, and an infusion speed of 0.005mm / min to 0.030mm / min, to obtain nanofibers; (3) mixing the nanofibers with water, and then subjecting them to high-speed crushing, and then subjecting them to high-pressure homogenization to obtain a mixed solution; the rotation speed of the high-speed crushing is 10000 rpm to 24000 rpm, and the time of the high-speed crushing is 10 min to 40 min; the pressure of the high-pressure homogenization is 500 bar to 1500 bar, and the time of the high-pressure homogenization is 10 min to 30 min; (4) adding inorganic particles to the mixed solution and dispersing them at high speed to obtain a coating slurry; (5) coating the coating slurry on the surface of the base film, and then baking to obtain the lithium ion battery separator; The functional coating comprises the following components in percentage by mass: 0.01% to 11.0% of nanofibers, 80% to 99.99% of inorganic particles, 0.01% to 10.0% of high-density surfactants, and 1% to 10% of adhesives.

2. The lithium-ion battery separator according to claim 1, characterized in that The functional coating also includes a polymer surfactant and / or an adhesive.

3. The lithium ion battery separator according to claim 1, characterized in that: The functional coating includes the following components in percentage by mass: 0.01% to 8.0% of nanofibers, 82% to 99% of inorganic particles, 0.02% to 5.0% of high-molecular-weight surfactants, and 2% to 8% of adhesives.

4. The lithium-ion battery separator according to claim 1, characterized in that The non-linear structure of the nanofibers includes bends and / or spirals; The protrusion structure includes a regular protrusion structure and / or an irregular protrusion structure; The shape of the inorganic particles includes at least one of a sphere, a regular polyhedron, and an irregular polyhedron.

5. The lithium ion battery separator according to claim 4, characterized in that: The shape of the protrusion structure includes streamline or spindle; The number of layers of the functional coating is 1 to 2; The thickness of the base film is 1 μm to 40 μm; The thickness of the functional coating is 0.1 μm to 19 μm; The nanofiber has a diameter of 10 nm to 1000 nm and a length of 20 μm to 30 μm; The average diameter D50 of the inorganic particles is 10nm to 3um; The pore sizes of the hierarchical porous structure are micropores and mesopores.

6. The lithium ion battery separator according to claim 2, characterized in that: The material of the nanofiber includes one or more of polyimide nanofiber, aramid nanofiber, polyetherimide nanofiber, polyamide-imide, polybenzimidazole nanofiber, polyetheretherketone nanofiber, polyphenylene sulfide nanofiber and polyvinylidene chloride; The material of the inorganic particles includes one or more of aluminum oxide, boehmite, magnesium hydroxide, silicon dioxide, silicon carbide, zirconium oxide and oxide solid electrolyte; The polymer surfactant includes one or more of polycarbonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium polyacrylate, polyvinyl alcohol, fluoroalkyl methoxy ether alcohol, fluoroalkyl ethoxy ether alcohol, alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ether, polyoxyethylene alkylamide, fluorinated carboxylates, triethyl phosphate, fluorinated sulfonates, potassium polyacrylate and polyethylene glycol; The adhesive comprises one or more of styrene-butadiene latex, styrene-acrylic latex, polyvinyl acetate, polyvinyl alcohol, polyethyl acrylate, polybutyl methacrylate, ethylene-vinyl acetate copolymer and polyurethane.

7. The lithium ion battery separator according to claim 2, characterized in that: Step (4) further includes: mixing the inorganic particles and water and adding a polymer surfactant to obtain a slurry; The nanofibers are mixed with water and then added to the slurry for high-speed dispersion for 5 minutes to 35 minutes, and then an adhesive is added to continue dispersion for 15 minutes to 40 minutes to obtain a coating slurry.

8. The lithium-ion battery separator according to claim 1, characterized in that: The baking temperature is 45°C to 90°C; The baking time is 1 min to 20 min.

Images